Solar cell module and method for manufacturing same

ABSTRACT

In order to ensure long-term reliability when a photovoltaic element is bent or curved to be deformed: 
     (1) In a method for manufacturing a solar cell module having a photovoltaic element encapsulated with a resin on a support member, the step is adopted which forms a bent portion in the photovoltaic element and in the support member, wherein the formation of the bent portion is performed while reducing a working pressure in the normal direction to a surface of the photovoltaic element; and 
     (2) In a solar cell module comprising a photovoltaic element comprising at least one photoactive semiconductor layer on a flexible substrate, at least a part of the flexible substrate is subjected to tensile deformation in the direction parallel to a surface of the substrate with a strain less than a critical strain to lower the fill factor of the photovoltaic element, whereby the photovoltaic element is deformed.

This application is a divisional of U.S. Ser. No. 09/062,642 filed Apr.20, 1998, now U.S. Pat. No. 6,215,060.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solar cell module and a method formanufacturing the same and more particularly to a wide variety of solarcell modules with high reliability in which a region including aphotovoltaic element is processed, and a method for manufacturing themodules.

2. Related Background Art

The solar cells popularly used at present are those of the type usingcrystal-based silicon and of the type using amorphous silicon. Amongothers, the amorphous silicon solar cells, in which silicon is depositedon a conductive metal substrate and a transparent, conductive layer isformed thereon, are promising, because they are inexpensive and lighterthan the solar cells of the crystal-based silicon, and they have goodimpact resistance and high flexibility. In recent years, the amorphoussilicon solar cells have been mounted on roofs and walls of buildings,taking advantage of the lightweight property, the good impactresistance, and the flexibility, which are the characteristics of theamorphous silicon solar cells. In this case, a support member(reinforcing sheet) is stuck to a non-light-receiving surface of a solarcell with an adhesive, and the composite is used as a building material.This sticking with a support member increases the mechanical strength ofa solar cell module, thus preventing warpage and distortion thereof dueto change in temperature. Particularly, since they can capture moresunlight, installation thereof on a roof is desirably conducted. Inapplications to the roofs, the conventional methods involved proceduresof mounting a frame on a solar cell, setting a stand on the roof, andinstalling the solar cells thereon; whereas the solar cell modules withthe support member stuck can be installed as roof materials directly onthe roof by bending the support member. This achieves great reductionsin the cost for raw materials and in the number of working steps,whereby inexpensive solar cell modules can be provided. In addition, thesolar cells become very lightweight, because neither the frame nor thestand is necessitated. Namely, the solar cells can be handled asmetallic roof materials, which are drawing attention recently because oftheir excellent mountability, light weight, and excellent earthquakeresistance.

For example, the roof material and solar cell combination moduleproposed in Japanese Patent Application Laid-open No. 7-302924 isexcellent in mountability because it is used in the same manner as theordinary roof materials; it is also easy to handle because conventionalmachines can be used. This solar cell module is, however, constructed insuch a structure that the photovoltaic element is located in a flatportion of a laterally-roofed flat-seam roof material and is notdeformed at all.

In recent years, however, the originality of individuals has becomeincreasingly valued, and this tendency is also the case for the buildingmaterials and solar cells. In order to produce the solar cells orbuilding materials that meet various needs and have a wide variety ofshapes, it is necessary to ensure the workability of all the regionsincluding the photovoltaic elements rather than to always keep theregions above the photovoltaic elements flat.

Japanese Patent Application Laid-open No. 8-222752 or No. 8-222753 orJapanese Patent Publication No. 6-5769 describes a corrugated solar cellmodule as an example responding to the need for variety. In either case,the photovoltaic element is arranged in a corrugated manner in order toincrease utilization efficiency of light, and the manufacturing methodthereof involves a procedure of sticking the photovoltaic elements to asteel sheet or the like worked in a corrugated sheet shape, with anadhesive.

On the other hand, there are reports on studies of the relation betweena-Si:H (hydrogenated amorphous silicon) layer and strain thereof.

For example, Appl. Phys. Lett. 54 (17), 1989, pp. 1678-1680, “Electricalproperties of hydrogenated amorphous silicon layers on polymer filmsubstrate under tensile stress,” reports a change of resistance in adark state where a tensile force is applied to a single film of a-Si:H(0.5 μm thick and mainly of i-type a-Si:H) deposited on a PET/substrate(100 μm thick). The detailed contents of this report are as follows.

Under the tensile force, the a-Si:H layer gradually increases itsresistance (reversible) because of the piezoresistance effect before0.7% strain is reached; however, it experiences a quick increase(irreversible) of resistance after 0.7% strain has been exceeded,because weak Si-Si bonds are broken. However, the a-Si:H layer withincreased resistance due to 0.7% or more strain can be restored byannealing at 150° C. for one hour.

Further, J. Appl. Phys. 66 (1), 1989, pp. 308-311, “Effect of mechanicalstrain on electrical characteristics of hydrogenated amorphous siliconjunctions,” reports the piezojunction effect of a-Si:H having the pinjunction. The detailed contents of this report are as follows.

When a-Si:H having the pin junction is distorted in parallel with thepin junction, 8% decrease of current takes place both in the forwarddirection and in the reverse direction under the tensile stress of 7500με (in the dark state). Further, 8% increase of current occurs under thecompressive stress of 7500 με.

There is, however, nothing described as to specific stress on thephotovoltaic element on the occasion of bending the photovoltaic elementinto the corrugated shape or the like in the above conventionaltechniques. Namely, they fail to describe either a displacement amountof substrate, a displacement amount of photovoltaic element, or adisplacement amount of solar cell module. There is nothing describedabout the effect of the stress and deformation and about theirreliability at all.

Under such circumstances, the production of solar cell modules in whichthe photovoltaic elements are shaped so as to be placed under stress ordeformed has been avoided; if a module is shaped, the reliability inthat shape must be always examined. Since many reliability tests mustusually be conducted for one product (a worked shape), much time isnecessary to make a commercially available product. This method is notsuitable for bringing the product to the commercial stage at a speedthat meets the need for present solar cells and building materialsrequired to provide a wide variety of products.

As described above, the following points need to be met in order toproduce a wide variety of solar cell modules with high reliability athigher speed.

(1) To define a specific, deformable region of the photovoltaic elementon the occasion of work of the region including the photovoltaicelement.

(2) To ensure long-term reliability where the photovoltaic element isdeformed.

SUMMARY OF THE INVENTION

The inventor found the following methods best after intensive andextensive research and development for achieving the above points.

(1) In a method for manufacturing a solar cell module having aphotovoltaic element encapsulated with a resin on a support member, thestep is adopted which forms a bent portion in the photovoltaic elementand in the support member, wherein the formation of the bent portion isperformed while reducing a working pressure in the normal direction to asurface of the photovoltaic element; and

(2) In a solar cell module comprising a photovoltaic element comprisingat least one photoactive semiconductor layer on a flexible substrate, atleast a part of the flexible substrate is subjected to tensiledeformation in the direction parallel to a surface of the substrate witha strain less than a critical strain to lower the fill factor(hereinafter referred to as F.F.) of the photovoltaic element, wherebythe photovoltaic element is deformed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a solar cell module according to thepresent invention, FIG. 1B is a cross-sectional view taken along theline 1B—1B of FIG. 1A, and FIG. 1C is an enlarged view of the portion 1Cof FIG. 1B;

FIG. 2A is a plan view of an example of a photovoltaic elementapplicable to the solar cell module of the present invention,

FIG. 2B is a cross-sectional view taken along the line 2B—2B of FIG. 2A,and

FIG. 2C is a cross-sectional view taken along the line 2C—2C of FIG. 2A;

FIG. 3 is a view showing layers stacked during production of a solarcell module;

FIG. 4A is a perspective view of a solar cell module, the edges of whichare bent, and

FIG. 4B is a perspective view of the finished solar cell module;

FIG. 5A is a plan view of an example of a cell block applicable to thesolar cell module of the present invention,

FIG. 5B is an enlarged view of the portion 5B of FIG. 5A, and

FIG. 5C is a cross-sectional view taken along the line 5C—5C of FIG. 5B;

FIG. 6A is a perspective view of a solar cell module according to thepresent invention,

FIG. 6B is a cross-sectional view taken along the line 6B—6B of FIG. 6A,and

FIG. 6C is an enlarged view of the portion 6C of FIG. 6B;

FIG. 7 is a cross-sectional view of the solar cell module under bendingwith a bender;

FIG. 8 is a perspective view of a solar cell module according to thepresent invention;

FIG. 9 is a cross-sectional view of the solar cell module under curvingwith a press working machine;

FIG. 10A is a plan view of a solar cell module according to the presentinvention, and

FIG. 10B is a cross-sectional view taken along the line 10B—10B of FIG.10A;

FIG. 11 is a view showing layers stacked in a solar cell module of acomparative example;

FIG. 12 is a schematic view showing a scratch resistance test;

FIG. 13 is a cross-sectional view of a flat-plate shaped solar cellmodule;

FIG. 14 is a graph showing the relation between maximum pressure exertedon the photovoltaic element and change in photoelectric conversionefficiency before and after processing where the photoelectricconversion efficiency before processing is 1;

FIG. 15 is a graph showing an example of strain during processing of aphotovoltaic element; and

FIG. 16 is a graph showing the relation between peak strain of a-Si:Hand F.F.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A to 1C are a perspective view, a cross-sectional view and apartial enlarged view of a solar cell module according to the presentinvention. In FIGS. 1A to 1C, reference numeral 101 designatesphotovoltaic elements, 102 a fibrous inorganic, compound, 103 atransparent, organic polymer compound as a front surface filler, 104 atransparent resin film located outermost, 105 a transparent, organicpolymer compound as a back surface filler, 106 a back surface insulatingfilm, and 107 a support member.

A processed shape adopted in the present invention will be described.First, a flat-plate solar cell module is produced, and thereafter it isbent so as to have a continuous bent portion as shown in FIGS. 1A to 1C.It is, however, noted that, although FIGS. 1A to 1C show an example ofthe solar cell module having the continuous bent portion, the inventionis not limited to this example; the solar cell module can be processedso as to have a bent portion only in a part thereof or so as to havemany depressed and projected portions.

By the manufacturing method according to the present invention, thephotovoltaic elements can be processed without damage. Specifically, themanufacturing method involves reducing the bending pressure in the stepof forming the bent portion, so as to produce the solar cell modulewithout damage to the photovoltaic elements. It can, therefore,manufacture solar cell modules with high reliability.

For example, as in FIGS. 1A to 1C, the large solar cell module can beprocessed into a roof material having steps of narrow working width.Therefore, the solar cell module becomes a roof material also excellentin the aesthetic sense and in mountability with less joint portionsbecause there is no need to provide each step with a joint portion. Inaddition, the photovoltaic elements can be arranged on the supportmember, irrespective of the working width, so that the rate ofphotovoltaic element per area can also be increased, whereby the outputfrom the solar cells can be extracted efficiently.

Further, the capability of processing the support member including theportions provided with the photovoltaic elements gives rise to thediversity of external configurations, without having to be limited tothat of FIGS. 1A to 1C, and permits production of original buildingmaterials excellent in the aesthetic sense.

Since the support member, even with the photovoltaic elements, can beprocessed in the same steps as the building materials using the normalsteel sheet, the conventional manufacturing apparatus can be usedwithout much change. This lowers the manufacturing cost.

(Method for Forming Bent Portion)

Since the portions where the photovoltaic elements exist are bent, it isnecessary to ensure the reliability of the photovoltaic elements. Theinventors found that it was desirable to provide means for reducing thebending pressure normally exerted on the surface of photovoltaicelements during work. More specifically, it was found that the pressureexerted on the photovoltaic element was desirably not more than 500kgf/CM².

FIG. 14 is a graph showing the relation between maximum pressure exertedon the photovoltaic element and change in the photoelectric conversionefficiency before and after processing where the photoelectricconversion efficiency before processing is 1. It is seen that theapplication of pressure greater than 500 kgf/cm² increases the damage tothe photovoltaic element, thereby resulting in significant lowering ofconversion efficiency and thus failing to ensure the reliabilityrequired for a solar cell module.

A conceivable method for manufacturing the solar cell module withoutexerting the processing pressure on the photovoltaic element is a methodfor sticking solar cell modules onto a support member preliminarilyprocessed. This processing method is, however, different from theordinary processing step using the ordinary steel sheet, so that thismanufacturing method has lower mass-productivity; in addition, thisprocessing method increases the cost, because it necessitates anothermaterial such as an adhesive.

Hence, the above formation of the bent portion is carried out desirablyas follows: a flat-plate solar cell module is first formed as shown inFIG. 13, and thereafter it is bent by a press molding machine, a rollerformer molding machine, or a bender molding machine.

The press molding machine can be applied readily to any shapes, even toirregular shapes, once molds are made. Thus the press molding machine issuitable for processing the building material as shown in FIG. 9. In thecase of molding by press work, the solar cell module is processed whilebeing placed between an upper mold and a lower mold. In this case, ifpressure over 500 kgf/cm² is exerted on the photovoltaic element, itwill damage the photovoltaic element, so as to degrade the reliabilityof the solar cell. The following methods should be employed in order toreduce the pressure.

A first method is a method for applying the pressure onto only theregion of the support member where the photovoltaic element of the solarcell module does not exist, so as to plastically deform a part or thewhole of the support member, thereby molding the bent portion. Thispermits the solar cell module to be processed without touching theregions above the photovoltaic elements at all.

Another method is a method for placing a buffer material of a sheet ofrubber, urethane, foam, nonwoven fabric, polymer resin, or the likebetween the press molds and the solar cell module. This scatters thepressure of the press molds to thereby decrease the pressure on thephotovoltaic elements.

A further effective method is a method for providing a clearance betweenthe solar cell module and the processing machine at the bottom deadcenter of the press. Namely, the solar cell module can be processedwithout imposing the pressure on the entire solar cell module. When thestep of forming the bent portion is done by press molding, theworkability is enhanced. Since this is generally accomplished using asteel sheet, the solar cell module can be easily processed.

The roller former molding machine is excellent in processing in thelongitudinal direction. The same molding machine is ready for steelsheets of different lengths. Particularly, the roller former can beapplied to a long steel sheet and complicated bending and is ready forhigh-speed work. Thus this is a method of high mass-productivity. Inthis case, it is also preferable to wrap rollers used in the rollerformer with a buffer material of a sheet of rubber, urethane, foam,nonwoven fabric, polymer resin, or the like in order to reduce thepressure on the photovoltaic element.

The bender bending machine can bend a material by simple devicestructure. It is effective for simple bending and bending of arelatively small steel sheet. However, since the radius of curvature ofa blade of the bender is normally small, the pressure is concentrated onthe photovoltaic element during bending thereon. To reduce the pressure,the buffer material is thus desirably used between the blade of thebender and the solar cell module. Preferred buffer materials are sheetsof rubber, urethane, foam, nonwoven fabric, polymer resin, and the like,as above. Another means to reduce the pressure is to increase the radiusof curvature of the blade of the bender to not less than 100 mm. Whenthe step of forming the bent portion is carried out by bending with thebender, the bent portion can be formed by this inexpensive and easymethod. Particularly, this method is effective to process a short solarcell module.

Further, in the case where the solar cell module is bent for use as aroof material, the support member is sometimes bent at edge portions ofthe solar cell module. FIGS. 1A to 1C show an example of such case,wherein one of two opposing edge portions is bent into thelight-receiving side, while the other is bent into thenon-light-receiving side. This bending greatly improves themountability, because, in the case of the roof material and solar cellcombination modules of the present invention being mounted from the eaveedge, they can be mounted simply by fitting the bent portions of theupper and lower solar cell modules adjacent to each other on a jointbasis. Since this bending obviates the need for the frame and standnecessitated in the conventional mounting methods for laying solar cellson a roof, this method can reduce cost largely and also reduce weight.When this bending is done using a roller former, the working speed canbe increased and further reduction of cost can be achieved.

When the solar cell module of the present invention is compared with theconventional one of the type wherein the solar cell module is mounted onthe building material, the solar cell module also functioning as thebuilding material of the invention does not necessitate the buildingmaterial and can thus be obtained at low cost.

(Relation Between Photovoltaic Element and Strain)

An experiment to show the relation between the photovoltaic element ofthe present invention and strain will be described in detail. Thephotovoltaic element used is of a configuration in which a back surfacereflective layer, a photoactive layer of amorphous siliconsemiconductors of the pin junction type, a transparent, conductivelayer, and a collector electrode are stacked on a substrate. Theexperiment was conducted using this photovoltaic element, and theresults of the experiment will be described. First, a strain gage wasstuck to the non-light-receiving surface of the substrate of thephotovoltaic element. After that, initial characteristics were measured.This sample was subject to tensile (expanding) stress (strain) whichpulled the photovoltaic element in the direction parallel to the surfaceof the substrate with a tensile tester. In this case, measurement wasconducted at each of peak strains up to 12000 με (1.2% elongation) ofthe substrate. Characteristics of samples with different strains weremeasured again in this way, and surfaces of the photovoltaic elementswere finally observed by an SEM (scanning electron microscope).

The strain can be classified into two types, peak strain appearingduring application of the tensile force and residual strain remainingeven after release of the tensile force (FIG. 15). If defects such ascracks occur in a-Si:H at the point of the peak strain during thetensile force application, the defects will not be compensated for evenby elimination of all of the residual strain. Therefore, when therelation between the deformable region of a photovoltaic element andstrain is considered, the peak strain is significant.

The results of the above experiment are shown in FIG. 16. Firstdescribed referring to FIG. 16 is a definition of the critical strainwhich lowers F.F. of the photovoltaic element. A graph is made to showthe relation between strain of the photovoltaic element and F.F. changerate. In that case, as shown in FIG. 16, the decline (lowering) of F.F.starts at a certain strain point. Since this decline of F.F. draws agentle curve, the critical strain which lowers F.F. is determined at anintersecting point of two tangent lines drawn as illustrated. In thecase of FIG. 16 using a-Si:H, the intersecting point between the twotangent lines is at 7000 με (0.7% strain). This means that F.F. startsdecreasing when the peak strain becomes 7000 με or more. Thus, forprocessing the photovoltaic element and ensuring the reliabilitythereof, the peak strain in the photovoltaic element should be desirablyless than the critical strain which lowers F.F. (0.7% in the case ofa-Si:H) during processing. In order to deform the photovoltaic elementunder this condition, the flexible substrate is made of a materialhaving a plastic deformation region less than the critical strain whichlowers F.F. (0.7% in the case of a-Si:H). The photovoltaic element isdeformed while the substrate is deformed under the strain less than thecritical strain which lowers F.F. (0.7% in the case of a-Si:H). Thisresults in a deformed photovoltaic element without degrading theperformance of the photoactive semiconductor layer on the substrate.

Here, F.F. is defined as follows: F.F.=maximum power (Pm)/(short circuitcurrent (Isc)×open circuit voltage (Voc)). The physical meaning thereofis a ratio of the power Pm actually taken out to a product of Voc, whichis a value where only the voltage is maximum, and Isc, which is a valuewhere only the current is maximum. An actual value of F.F. is determinedby forward characteristics of pn junction, and thus F.F. will decreaseif a leak current flows through defects contained in the semiconductorsubstrate used and defects produced during production of an junction orduring production steps thereafter. This will result in decreasing theoutput that is expected. From this aspect, decrease in F.F. after thetensile force application test indicates occurrence of defects in thesemiconductor layer due to the tensile test.

As also seen from the above, in the case of a-Si:H, when the peak strainis not less than 0.7%, i.e., when a photovoltaic element has a strainnot less than the critical strain which lowers F.F., it is believed thatdefects have been generated in the photovoltaic element.

When the photovoltaic element was observed from the light-receiving sideby an SEM, many cracks were observed in the normal direction to theflexible substrate in portions where the strain was not less than thecritical strain which lowers F.F. From the degradation incharacteristics of the solar cell at this time, it is supposedinterfacial separation also occurred between films in the configurationof substrate/metal layer/transparent electrode layer/activesemiconductor layers/transparent electrode or within the activesemiconductor layers.

Places where the strain appears in the bending as shown in FIGS. 1A to1C are top and bottom portions in the stepped shape. The maximum strainappears at the top portions of the stepped shape. The strain alsoappears in the bottom portions, but it is very small.

FIGS. 1A to 1C show the example in which the solar cell module is bentin the continuous step shape, but the invention is by no means limitedto this example. For example, only a part of the solar cell module canbe bent, the solar cell module can be bent so as to have many depressedand projected portions, or a flat-plate solar cell module can beprocessed as to suffer tensile stress in the flat shape, as long as theprocessing causes plastic deformation while keeping the strain of theflexible substrate less than the critical strain which lowers F.F. Sincethe solar cell module can be worked irrespective of presence or absenceof the photovoltaic element, a large solar cell module can be workedinto a roof material of the step shape with a narrow working width, forexample, as shown in FIGS. 1A to 1C, and the roof using such solar cellmodules will be excellent in the aesthetic sense and also excellent inmountability with less joint portions because there is no need toprovide a joint portion for each step. Further, the arrangement of thephotovoltaic elements does not have to be changed depending upon theconfiguration of the solar cell module, and the same flat-plate solarcell module can be processed in a variety of shapes. Therefore, thesolar cell module is excellent in workability and productivity.Specifically, considering processing of the solar cell module providedwith the support member, the support member is often made of a materialhaving higher rigidity than the substrate, and it is thus hard tomaintain the processed shape of the solar cell module by only plasticdeformation of the flexible substrate. In that case, an example ofprocessing the shape of a solar cell module is plastically deformingonly portions no photovoltaic element is present on the support member,thereby maintaining the shape of the entire support member. By thismethod, the solar cell module provided with the support member can beprocessed as a solar cell module while keeping the strain of theflexible substrate less than the critical strain which lowers F.F., andthe shape thereof can be maintained thereby; therefore, the solar cellmodule can be excellent both in reliability and in the aesthetic sense.

Described below are the photovoltaic element used in the presentinvention and materials for covering the photovoltaic element.

(Photovoltaic Element 101)

FIGS. 2A to 2C show an example of the photovoltaic element applicable tothe solar cell module according to the present invention. Referencenumeral 201 designates a conductive substrate, 202 a back surfacereflective layer, 203 a photoactive semiconductor layer, 204 atransparent, conductive layer, 205 a collector electrode, and 206 outputterminals.

The conductive substrate 201 functions as a substrate of thephotovoltaic element and also functions as a lower electrode. Theconductive substrate 201 may be made of a material selected fromsilicon, tantalum, molybdenum, tungsten, stainless steel, aluminum,copper, titanium, a carbon sheet, a lead-plated iron sheet, and a resinor ceramic film with a conductive layer formed thereon.

As the back surface reflective layer 202 on the above-stated conductivesubstrate 201, there may be formed a metal layer, or a metal oxidelayer, or a combination of a metal layer and a metal oxide layer. Themetal layer is made, for example, of Ti, Cr, Mo, W, Al, Ag, or Ni, andthe metal oxide layer is made, for example, of ZnO, TiO₂ or SnO₂. Amethod for forming the above metal layer and metal oxide layer isselected from the resistance heating vapor deposition method, theelectron beam vapor deposition method, the sputtering method, and so on.

The photoactive semiconductor layer 203 is a section for effectingphotoelectric conversion. Specific examples of materials for thephotoactive semiconductor layer 203 are pn junction type polycrystallinesilicon, pin junction type amorphous silicon, and compoundsemiconductors including CuInSe₂, CuInS₂, GaAs, CdS/CU₂S, CdS/CdTe,CdS/InP, and CdTe/Cu₂Te. The photoactive semiconductor layer is made bysheeting molten silicon or by heat treatment of amorphous silicon in thecase of polycrystalline silicon; or by plasma enhanced CVD using silanegas or the like as a raw material in the case of amorphous silicon; orby ion plating, ion beam deposition, vacuum vapor deposition,sputtering, or electrodeposition in the case of the compoundsemiconductors.

The transparent, conductive layer 204 serves as an upper electrode ofthe solar cell. The transparent, conductive layer 204 is made of amaterial selected, for example, from In₂O₃, SnO₂ In₂O₃—SnO₂ (ITO), ZnO,TiO₂, Cd₂SnO₄, and crystalline semiconductor layers doped with a highconcentration of impurities. A method for forming the transparent,conductive layer 204 is selected from resistance heating vapordeposition, sputtering, spraying, CVD, and an impurity diffusing method.

On the transparent, conductive layer, there may be provided thecollector electrode 205 (grid) of a grating pattern in order toefficiently collect electric currents. Specific materials for thecollector electrode 205 are, for example, Ti, Cr, Mo, W Al, Ag, Ni, Cu,Sn, and conductive pastes including a silver paste. A method for formingthe collector electrode 205 is selected from sputtering with a maskpattern, resistance heating, CVD, first evaporating a metal film overthe entire surface and thereafter patterning it by removing unnecessaryportions by etching, directly forming the grid electrode pattern byphoto-CVD, first forming a mask of a negative pattern of the gridelectrode pattern and then effecting plating thereon, and printing aconductive paste. The conductive paste is usually selected from those inwhich fine powder of silver, gold, copper, nickel, carbon, or the likeis dispersed in a binder polymer. As the binder polymer, there may beincluded, for example, polyester, epoxy, acrylic, alkyd, polyvinylacetate, rubber, urethane, and phenol resins.

Finally, the positive output terminal 206 a and negative output terminal206 b are attached to the collector electrode and to the conductivesubstrate, respectively, for taking out the electromotive force. Theoutput terminal is attached to the conductive substrate by a method forsticking a metal member such as a copper tab thereto by spot welding orsoldering. The output terminal is attached to the collector electrode bya method for electrically connecting a metal member thereto by aconductive paste 207 or solder. When attached to the collector electrode205, an insulating member 208 is desirably provided in order to preventthe output terminal from touching the conductive metal substrate and thesemiconductor layer, thereby causing short circuit.

The photovoltaic elements produced by the above techniques are connectedin series or in parallel, depending upon desired voltage or electriccurrent. When they are connected in series, the positive output terminalof one cell is connected to the negative output terminal of a next cell.When they are connected in parallel, the output terminals of the samepole are connected to each other. Different from these examples, it isalso possible to integrate photovoltaic elements on an insulatedsubstrate to obtain a desired voltage or current.

A material for the metal member used for connection of the outputterminals and the elements is selected desirably from copper, silver,solder, nickel, zinc, and tin, taking account of high conductivity, thesoldering property, and cost.

(Fibrous Inorganic; Compound 102)

Next described is the fibrous inorganic compound 102 soaked in thesurface filler. First, the surface of the solar cells of amorphoussilicon is covered by a plastic film in order to take full advantage ofits flexibility. In this case, however, the surface is much lessresistant to exterior scratching than in the case of the outermostsurface being covered by glass.

The solar cell modules, particularly modules mounted on the roof or thewall of a house, are required to have flame resistance. The surfacecovering material, however, becomes very flammable with a large amountof transparent, organic polymer resin contained therein. On the otherhand, it cannot protect the photovoltaic elements from external impactif the amount of polymer resin is small. In order to protect thephotovoltaic elements sufficiently from the external environments by asmall amount of the resin, transparent organic polymer resin in whichthe fibrous inorganic compound is soaked is used as the surface coveringmaterial.

The fibrous inorganic compound is selected specifically from nonwovenfabric of glass fiber, woven fabric of glass fiber, glass filler, and soon. Particularly, the nonwoven fabric of glass fiber is used preferably.The glass fiber fabric is expensive and hard to impregnate. When theglass filler is used, there is little increase in the scratchresistance, and it is not easy to cover the photovoltaic elements with asmaller amount of the transparent organic polymer resin. It is alsodesirable as to long-term use to treat the fibrous inorganic compoundwith a silane coupling agent or an organic titanate compound, similar tothose used in the transparent organic polymer resin, in order to assuresufficient adhesiveness.

(Filler 103)

The transparent organic polymer resin used for the surface filler 103 isnecessary for covering the unevenness of the photovoltaic elements withthe resin, for protecting the photovoltaic elements from severe externalcircumstances such as temperature change, humidity, and impact, and forensuring adhesion between the surface film and the elements. Therefore,it needs to be excellent in weather resistance, adhesion, fillingproperty, heat resistance, low temperature resistance, and impactresistance. Resins satisfying these requirements includepolyolefin-based resins such as ethylene-vinyl acetate copolymers (EVA),ethylene methyl acrylate copolymers (EMA), ethylene ethylacrylatecopolymers (EEA) and butyral resins, urethane resins, silicone resins,and so on. Among them, the EVA copolymers are preferably used, becausethey have well-balanced physical properties for use in a solar cell.

Since EVA copolymers, if not crosslinked, readily undergo deformation orcreep in use at high temperature because of their low thermaldeformation temperature, they should desirably be crosslinked in orderto enhance the heat resistance. In the case of the EVA, it is general toeffect crosslinking using an organic peroxide. The crosslinking with theorganic peroxide is made in such a way that free radicals produced fromthe organic peroxide draw hydrogen and halogen atoms out of the resin toform C—C bonds. The known methods for activating the organic peroxideinclude thermal decomposition, redox decomposition, and ionicdecomposition. In general, the thermal decomposition method is favorablyadopted. Specific examples of the chemical structure of the organicperoxide are roughly classified into hydroperoxide, dialkyl (allyl)peroxide, diacyl peroxide, peroxy ketal, peroxy ester, peroxy carbonate,and ketone peroxide.

An amount of the organic peroxide added is in the range of 0.5 to 5parts by weight per 100 parts by weight of the filler resin.

When the above organic peroxide is used in combination with the filler,the crosslinking and thermocompression bonding can be achieved underheating and pressure application. The heating temperature and time canbe determined depending upon the thermal decomposition temperaturecharacteristics of the respective organic peroxides. In general,application of heat and temperature is stopped at the temperaturereaches 90%, more preferably not less than 95%. The gel percentage ofthe filler by this is preferably not less than 80%. The gel percentageherein is given by the following equation.

Gel percentage=(weight of the undissolved/original weight of sample)×100(%)

Namely, when the transparent organic polymer resin is extracted with asolvent of xylene or the like, the part gelled by crosslinking is noteluted but only the non-crosslinked sol part is eluted. The gelpercentage of 100% means completion of perfect crosslinking. Only theundissolved gel part can be obtained by taking out the sample remainingafter the extraction and evaporation of xylene therefrom.

If the gel percentage is less than 80%, the resultant resin will havelowered heat resistance and creep resistance and will pose a problem inuse under high temperature, for example, in summer.

For efficiently advancing the above crosslinking reaction, it is desiredto use triallyl isocyanurate (TAIC), which is called a crosslinkingassistant. An amount of the crosslinking assistant added is normally inthe range of 1 to 5 parts by weight per 100 parts by weight of thefiller resin.

The material of the filler used in the present invention is excellent inweather resistance, but an ultraviolet absorbing agent may also be addedin order to further enhance weather resistance or in order to protectthe layer located below the filler. The ultraviolet absorbing agent canbe selected from the known compounds and is preferably selected fromlow-volatile ultraviolet absorbers, taking account of use environmentsof the solar cell modules. If a light stabilizer is also added togetherwith the ultraviolet absorber, the filler will become more stable tolight. Specific chemical structures of ultraviolet absorbers are roughlyclassified into salicylic acid-based, benzophenone-based,benzotriazole-based, and cyanoacrylate-based absorbers. It is preferredto add at least one of these ultraviolet absorbers.

As a method for imparting weather resistance other than the use of theabove ultraviolet absorber, it is known that use of ahindered-amine-based light stabilizer is available. Thehindered-amine-based light stabilizer does not absorb ultraviolet light,different from the ultraviolet absorber, but it can demonstrate a greatsynergistic effect when used together with the ultraviolet absorber. Anamount of the stabilizer added is normally approximately 0.1-0.3 part byweight per 100 parts by weight of the resin. There are, of course, lightstabilizers other than the hindered-amine-based stabilizers, but themost of them are colored and thus are not desirable for use in thefiller of the present invention.

Further, an antioxidant may be added for improving the thermalresistance and thermal workability. An amount of the antioxidant addedis preferably 0.1-1 part by weight per 100 parts by weight of the resin.Chemical structures of antioxidants are roughly classified intomonophenol-based, bisphenol-based, polymer-type-phenol-based,sulfur-based, and phosphoric-acid-based inhibitors.

If the solar cell modules are assumed to be used under severecircumstances, it will be preferable to enhance the adhesive strengthbetween the filler and the photovoltaic elements or the surface film.The adhesive strength can be enhanced by adding a silane coupling agentor an organic titanate compound to the filler. An amount of the additiveis preferably 0.1 to 3 parts by weight per 100 parts by weight of thefiller resin and more preferably 0.25 to 1 part by weight per 100 partsby weight of the filler resin. Moreover, addition of the silane couplingagent or the organic titanate compound into the transparent organicpolymer is also effective for enhancing the adhesive strength betweenthe transparent organic/polymer compound and the fibrous inorganiccompound therein.

On the other hand, the surface filler needs to be transparent in orderto prevent decrease in the quantity of light reaching the photovoltaicelements as much as possible. Specifically, the light transmittancethereof is preferably 80% or more and more preferably 90% or more in thevisible light wavelength region from 400 nm to 800 nm. For facilitatingincidence of light from the atmosphere, the refractive index of thefiller at 25° C. is preferably 1.1 to 2.0 and more preferably 1.1 to1.6.

(Surface Resin Film 104)

Since the surface resin film 104 employed in the present invention islocated in the outermost layer of the solar cell module, it needs toexhibit long-term reliability under outdoor exposure of the solar cellmodule, including the weather resistance, pollution resistance, andmechanical strength. The resin film used in the present inventionincludes a fluororesin film, an acrylic resin film, and so on. Amongthem, the fluororesin films are favorably used because of theirexcellent weather resistance and pollution resistance. Specific examplesof the fluororesins are polyvinylidene fluoride resins, polyvinylfluoride resins, tetrafluoroethylene-ethylene copolymers, and so on. Thepolyvinylidene fluorid resins are excellent in terms of weatherresistance, while the tetrafluoroethylene-ethylene copolymers areexcellent in terms of weather resistance, mechanical strength, andtransparency.

For improving the adhesion to the filler, the surface film is desirablysubjected to a surface treatment such as corona treating, plasmatreating, ozone treating, UV irradiation, electron beam irradiation, orflame treating. Specifically, the wetting index of the surface on thephotovoltaic element side is preferably 34 dyne to 45 dyne. If thewetting index is not more than 34 dyne, the adhesive strength will notbe sufficient between the resin film and the filler, and separation willoccur between the filler and the resin film. Further, when the resinfilm is a tetrafluoroethylene-ethylene copolymer film, it is difficultto achieve the wetting index over 45 dyne.

If the resin film is an oriented film, cracks will appear. In the casewherein the edge portions of the solar cell module are bent as in thepresent invention, the film would be broken at the bent portions so asto promote peeling off of the covering material and intrusion of waterin those portions, thereby degrading the reliability. For this reason,the resin film is desirably a non-oriented film. Specifically, thetensile elongations at break according to ASTM D-882 testing method arepreferably 200% to 800%, both in the longitudinal direction and in thetransverse direction.

(Back Surface Filler 105)

The back surface filler 105 is provided in order to achieve adhesionbetween the photovoltaic elements 101 and the insulating film 106 on theback surface. Preferred materials for the back surface filler 105 arethose capable of ensuring sufficient adhesion to the conductivesubstrate, excellent in the long-term durability, resistant to thermalexpansion and thermal contraction, and flexible. A suitable material isselected from hot melt materials such as EVA, ethylene-methyl acrylatecopolymer (EMA), ethylene-ethyl acrylate copolymers (EEA), polyethylene,or polyvinyl butyral, a two sided adhesive tape, an epoxy adhesivehaving flexibility, and so on. In addition, for enhancing the adhesivestrength to the support member and the insulating film, the surface ofthese adhesives may be coated with a tackifier resin. These fillers areoften the same materials as the transparent polymer resins used for thesurface filler 103. For simplification, it is also possible to use amaterial in which the adhesive layer described above is preliminarilylaid integrally on the both sides of the insulating film.

(Insulating Film 106)

The insulating film 106 is necessary for maintaining the electricalinsulation between the conductive metal substrate of the photovoltaicelement 101 and the outside. Preferred materials are those capable ofensuring the sufficient electrical insulation to the conductive metalsubstrate, excellent in long-term durability, resistant to thermalexpansion and thermal contraction, and flexible. A stable film isselected from polyamide, polyethylene terephthalate, polycarbonate, andso on.

(Support Member 107)

To the outside of the back surface covering film, the support member 107is stuck in order to increase the mechanical strength of the solar cellmodule, in order to prevent distortion or warpage due to temperaturechange, or in order to realize the solar cell module which functionsalso as a roof material. A preferred material for the support member 107is selected, for example, from a painted galvanized iron sheet coveredby an organic polymer resin with excellent weather resistance and rustresistance, a plastic sheet, an FRP (glass fiber reinforced plastic)sheet, and so on.

(Formation of Module)

FIG. 3 is a drawing showing a stacking configuration of layers whichform the solar cell module. Specifically, the photovoltaic element 301,inorganic filler compound 302, surface filler 303, surface resin film304, back surface filler 305, insulating film 306, and support member307 are stacked in the order illustrated in the figure or in the reverseorder and are pressed under heat by a vacuum laminating apparatus,thereby obtaining the solar cell module 308. The heating temperature andheating period during the pressing are determined to be a temperatureand a period sufficient to progress the crosslinking reaction.

Since the step of encapsulating the photovoltaic element is carried outat the same time as the step of fixing the encapsulated photovoltaicelement to the support member, a low-cost solar cell module can beobtained. Namely, the covering step of the solar cell module can beconducted easily by the simple apparatus, and the productivity is thusincreased.

The solar cell module 308 produced in this way is processed so as tohave the bent portion by the press molding machine, the roller formermolding machine, or the bender molding machine, thereby obtaining thesolar cell module of the present invention.

The solar cell modules of the present invention are used together with apower converting device, so as to compose a power generation system. Thepower converting device performs such control as to always maximize theoutput from the solar cell modules. The power generation system may havean interconnecting function to a commercial power system.

EXAMPLES Example 1-1

[Photovoltaic Element]

First, amorphous silicon (a-Si) solar cells (photovoltaic elements) areproduced. The producing procedures will be described referring to FIGS.2A to 2C.

On a cleaned stainless steel substrate 201, an Al layer (5000 Å thick)and a ZnO layer (5000 Å thick) are successively formed by sputtering toform a back surface reflective layer 202. Then a tandem type a-Siphotoelectric conversion semiconductor layer 203 is formed in the layerstructure of n-layer 150 Å thick/i-layer 4000 Å thick/p-layer 100 Åthick/n-layer 100 Å thick/i-layer 800 Å thick/p-layer 100 Å thick bymaking the n-type a-Si layers from a gaseous mixture of SiH₄, PH₃, andH₂, the i-type a-Si layers from a gaseous mixture of SiH₄ and H₂, andthe p-type microcrystalline Si (i.e., μc-Si) layers from a gaseousmixture of SiH₄, BF₃ and H₂ by the plasma CVD method. Next, In₂O₃ thinfilm (700 Å thick) is formed as a transparent, conductive layer 204 byevaporating indium (In) in an O₂ atmosphere by the resistance heatingmethod. Further, a grid electrode 205 for collection of current isformed by screen printing of a silver paste. In a final step, a coppertab as a negative terminal 206 b is attached to the stainless-steelsubstrate with solder 207, and a tape of tin foil as a positive outputterminal 206 a is attached to the collector electrode 205 with solder207 so as to form the output terminals, thus obtaining a photovoltaicelement.

[Cell Block]

A method for producing a solar cell block by connecting the cellsdescribed above in the 5 serial×2 parallel configuration will bedescribed referring to FIGS. 5A to 5C.

First produced are two sets of 5-series cell blocks. Five cells arearranged on a horizontal line, and thereafter the positive terminal, 503a of one of adjacent cells is connected through copper tab 504 withsolder 505 to the negative terminal 503 b of the other cell. By this,the five cells are connected in series, thereby forming aseries-connected cell block. The copper tab connected to the outputterminal of the end cell is routed to the back surface so as to form aback surface collector electrode to permit the output to be taken outthrough a hole in the back surface covering layer as describedhereinafter. In FIG. 5C, numeral 502 designates insulating films forelectric isolation. Then two series-connected cell blocks are juxtaposedand the same poles of the back surface collector electrodes of theseries-connected cell blocks are connected in parallel using copper tabsand solder. A solar cell block is completed in this way. [Formation ofmodule]

FIGS. 6A to 6C show a method for forming the solar cell module bycovering the photovoltaic elements (cell blocks) connected in paralleland in series. The solar cell module is produced by preparing cell block601, fibrous inorganic compound (40 g/m²) 602, surface filler 603,surface resin film 604, fibrous inorganic compound (20 g/m²) 605, backsurface laminate film 606, and support member 607 and stacking them inthe order of FIG. 6C. A decorative tape 608 is laid on the positiveoutput terminal in order to conceal the positive output terminal 609 ofthe cell block 601.

<Fibrous Inorganic Compound 602>

Prepared is a nonwoven fabric of glass fiber having the basis weight of40 g/M², the thickness of 200 μm, and the fiber diameter of 10 μm andcontaining 4.0% of acrylic resin as a binder.

<Fibrous Inorganic Compound 605>

Prepared is a nonwoven fabric of glass fiber having the basis weight of20 g/m², the thickness of 100 μm, and the fiber diameter of 10 μm andcontaining 4.0% of acrylic resin as a binder.

<Surface Filler 603>

Prepared is an EVA sheet of 460 μm in thickness formulated by blendingan ethylene-vinyl acetate copolymer (25 wt % vinyl acetate), acrosslinking agent, an ultraviolet absorber, an antioxidant, and a lightstabilizer.

<Surface Resin Film 604>

A non-oriented ethylene-tetrafluoroethylene (ETFE) film of 50 μm inthickness is prepared as a surface resin film. A surface of the film tocontact the filler 603 is preliminarily processed by plasma treating.

<Back Surface Laminate Film 606>

Prepared as the laminate film 606 is a laminate film of the totalthickness 500 μm obtained by integrally laminating an ethylene-ethylacrylate copolymer (EEA) (200 μm thick) and a polyethylene (PE) resin(25 μm thick) as an adhesive layer and a biaxially oriented polyethyleneterephthalate film (PET) (50 μm thick) as an insulating film in theorder of EEA/PE/PET/PE/EEA.

<Support Member 607

Prepared as the support member 607 is a steel sheet obtained by coatingone surface of a galvalium sheet ion (an aluminum-zinc alloy platedsteel sheet of aluminum 55%, zinc 43.4%, and silicon 1.6%) with apolyester-based paint and the other surface with a polyester-based paintcontaining glass fibers. The thickness of the steel sheet is 400 μm.

<Decorative Tape 608>

As the decorative tape 608, is prepared a film of EVA/PET/EVA obtainedby integrally laminating EVA films (460 μm thick) on the both sides ofpolyethylene terephthalate (PET) film (50 μm thick and black colored).

<Formation of Module>

This lamination is heated in vacuum using a laminating apparatus of thesingle vacuum system, thereby forming a flat-plate solar cell module.The vacuum conditions include an evacuation rate of 76 Torr/sec and avacuum of 5 Torr for 30 minutes. After that, the laminating apparatus isput in a hot-air oven at 160° C. to be heated for 50 minutes. The EVA isthen maintained at 140° C. or more for 15 minutes or more. This causesthe EVA to be melted and crosslinked.

[Processing with Roller Former]

Next, as shown in FIG. 4A, two opposing edges of the solar cell moduleare bent by the roller former so as to form seam-joint portions torealize the engaging function of roof material. In this case, the solarcell module is bent while preventing the rollers from touching thephotovoltaic element portions.

[Processing with Bender]

Next, as shown in FIG. 4B, the support member is bent by the bender,irrespective of presence or absence of the photovoltaic element.

FIG. 7 is a drawing showing the details of the bending by the bender. Aurethane sheet 702 is used as a buffer material between a lower blade704 of the bender and the solar cell module 701 and between an upperblade 703 of the bender and the solar cell module 701. The thickness ofthe urethane sheet 702 used is 2 mm, and the clearance between the upperblade 703 and the lower blade 704 is 8 mm.

The bending is done so that the processed shape has the passed width of180 mm and the height of 30 mm.

In the last step, wires for taking the power out are attached to theback surface of the solar cell module. The support member ispreliminarily perforated in terminal-out portions of the solar cellgroup, and the positive and negative output terminals are taken outthrough the holes. Further, each terminal-out portion is provided with apolycarbonate junction box 610 for insulation protection andwaterproofness. Cables used are cable lines each having a connector atthe tip.

Example 1-2

The solar cell module is produced in the same manner as in Example 1-1except that the blade of the bender having the radius of curvature of300 mm is used as means for reducing the pressure during bending ofregions above the photovoltaic elements by the bender.

Example 1-3

The solar cell module of Example 1-3 is shown in FIG. 8.

The photovoltaic elements are made in the same manner as in Example 1-1and the other steps are described below.

<Cell Block 801>

The five cells described above are connected in series to produce asolar cell block 801. The method for producing the block is the same asin Example 1-1.

<Formation of Module>

The flat-plate solar cell module is made of the above five-series solarcell block in the same manner as in Example 1-1.

<Bending of Edge Portions>

The four corners of the flat-plate solar cell module are cut by cornershears. After that, the shorter edges are folded 180° to formshorter-edge bent portions 802 in order to reinforce the shorter edges;the longer edges are bent 90° on the light-receiving side by the benderto form longer-edge bent portions 803. The height of upright parts ofthe longer-edge bent portions 803 is 25 mm.

<Press Processing>

The bent portion is formed by the press processing shown in FIG. 9. Thepress processing is conducted by placing the solar cell module 901between a lower mold 904 having a projected portion and an upper mold903 having a depressed portion. On that occasion, an urethane sheet 902having a thickness of 5 mm is interposed between the molds and the solarcell module in order to reduce the vertical pressure exerted on thephotovoltaic elements by the press. Namely, the stacking order in thepress processing is the lower mold 904/the urethane sheet 902/the solarcell module 901/the urethane sheet 902/the upper mold 903.

Example 1-4

The solar cell module of Example 1-4 is shown in FIGS. 10A and 10B.

The flat-plate solar cell module is made in the same manner as inExample 1-3.

(Press Processing>

Depressed portions 1002 are formed by press processing. The solar cellmodule is pressed while being interposed between a lower mold havingdepressed portions and an upper mold having projected portions, thedepressed portions and projected portions being arrayed in a matrix of4×7 squares each having the size of 150 mm×150 mm as shown in FIGS. 10Aand 10B. On that occasion, an urethane sheet of 5 mm in thickness isinterposed between the molds and the solar cell module in order toreduce the vertical pressure exerted on the photovoltaic elements by thepress. Namely, the stacking order in the press processing is the lowermold/the urethane sheet/the solar cell module/the urethane sheet/theupper mold.

Comparative Example 1-1

The solar cell module is produced in the same manner as in Example 1-1except that the urethane sheet for reducing the pressure exerted by thebender is not used.

Comparative Example 1-2

The solar cell module is produced in the same manner as in Example 1-3except that the urethane sheet for reducing the pressure exerted by thepress is not used.

Comparative Example 1-3

The solar cell module is produced in the same manner as in Example 1-4except that the urethane sheet for reducing the pressure exerted by thepress is not used.

Comparative Example 1-4

The cell block is formed in the same manner as in Example 1-1. Stepsafter the formation of cell block will be described below in detail.

[Formation of Module]

The solar cell module is produced without using the support member inExample 1-1. Specifically, as shown in FIG. 11, the solar cell module ismade by preparing a cell block 1101, a fibrous inorganic compound (40g/m²) 1102, a transparent organic polymer resin 1103 on thelight-receiving side, a surface resin film 1104, a fibrous inorganiccompound (20 g/m²) 1105, a back surface adhesive 1106, and an insulatingfilm 1107 and stacking them as illustrated.

<Back Surface Adhesive 1106>

The back surface adhesive used is the same resin as the organic polymerresin on the light-receiving side.

<Insulating Film 1107>

The insulating film used is a polyethylene terephthalate film (PET) (50μm thick).

[Sticking]

The flat-plate solar cell module after the formation of module is stuckto a steel sheet prepared as a roof material preliminarily processed asto have a bent portion, thus making the solar cell module.

The solar cell modules of the respective examples are evaluated as tothe following items. The results are shown in Table 1 below.

TABLE 1 After temp/humid Initial After hi-temp and hi-humid test cycletest external external conversion external conversion workabilityappearance appearance efficiency appearance efficiency Scratchresistance Ex 1-1 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Ex 1-2 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Ex 1-3 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚⊚ Ex 1-4 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Comp Ex 1-1 ⊚ X X Δ X Δ ⊚ Comp Ex 1-2 ⊚ X X Δ X Δ⊚ Comp Ex 1-3 ⊚ X X Δ X Δ ⊚ Comp Ex 1-4 X ⊚ X ⊚ X ⊚ ⊚

Workability

The workability is examined from aspects of processing speed andoperability on the occasion of formation of the solar cell moduleprocessed so as to have the bent portion in a part or the whole of thesupport member including the photovoltaic elements. The results ofexamination are shown in Table 1, based on the following criteria.

⊚ The time necessary for processing one module is 1 sec to 30 sec, andthe module is thus considered to have very high mass-productivity andgood operability.

∘: The time necessary for processing one module is 30 sec to 60 sec, andthe module is thus considered to be of slightly inferiormass-productivity and operability but to be mass-producible.

×: The time necessary for processing one module is longer than 60 sec,and the module is considered to have poor mass-productivity andoperability and to be incapable of being mass-produced.

Initial External Appearance

The solar cell modules having the bent portion (in the final form) areevaluated as to the initial external appearance, including failure infilling and flaws on the surfaces of the solar cells. The evaluationresults are shown in Table 1, based on the following criteria.

⊚: No defect is present in the external appearance.

∘: Some defects are present in the external appearance but pose noproblem in practical use.

×: Failure in filling and flaws on the surface are extreme and thus thedefects are very large in the external appearance.

If any other defect is observed, a comment is given.

High Temperature and High Humidity Test

The solar cell modules are placed under the circumstance of 85° C./85%(relative humidity) for 3000 hours and thereafter the solar cell modulesare taken out. Change of appearance is observed visually. Further, theconversion efficiency is measured under irradiation of light AM 1.5: 100MW/Cm², and a change rate is calculated from the initial value beforethe test. The evaluation results are shown in Table 1, based on thefollowing criteria. (Appearance)

∘: No defect is present in the external appearance.

Δ: Some defects are present in the external appearance but pose noproblem in practical use.

×: Considerable exfoliation or the like appears and defects areextremely large in the external appearance.

(Conversion Efficiency)

∘: The change of conversion efficiency is less than 1.0%.

∘: The change of conversion efficiency is not less than 1.0% and lessthan 3.0%.

Δ: The change of conversion efficiency is not less than 3.0% and lessthan 5.0%.

×: The change of conversion efficiency is not less than 5.0%.

Temperature/Humidity Cycle Test

The solar cell modules are subjected to 100 temperature/humidity cycletests of −40° C./0.5 hour: 85° C./85% (relative humidity)/20 hours, andthereafter the solar cell modules are taken out. Change of externalappearance is observed visually. The conversion efficiency is measuredunder irradiation of light AM 1.5: 100 mw/Cm², and the change rate iscalculated from the initial value before the test. The evaluationresults are shown in Table 1, based on the following criteria.

(Appearance)

∘: No defect is present in the external appearance.

Δ: Some defects are present in the external appearance but pose noproblem in practical use.

×: Considerable exfoliation or the like appears and defects areextremely large in the external appearance.

(Conversion Efficiency)

⊚: The change of conversion efficiency is less than 1.0%.

∘: The change of conversion efficiency is not less than 1.0% and lessthan 3.0%.

Δ: The change of conversion efficiency is not less than 3.0% and lessthan 5.0%.

×: The change of conversion efficiency is not less than 5.0%.

Scratch Resistance

By the method as shown in FIG. 12, a portion which seems to, have thelargest unevenness in the surface of a solar cell module 1201 mounted ona metal member is scratched under the weight of 2 pounds and 5 poundswith test blade 1202. The solar cell modules are evaluated as to whetherthe surface covering material subjected to the scratch can maintaininsulation from the outside. Determination is made in the followingmanner: the module is soaked in an electrolytic solution of theconductivity of 3000 Ω·cm, and the voltage of 2200 V is applied betweenthe element and the solution. If a leak current exceeds 50 μA, themodule is determined to be a reject. The evaluation results are given inTable 1, based on the following criteria.

⊚: Acceptance in the 5-pound test

∘: Acceptance in the 2-pound test

×: Rejection in the 2-pound test

As apparent from Table 1, the solar cell modules of the examples of theinvention demonstrate excellent workability and sufficientmass-productivity. As for the initial appearance of the final form, theyhave no such defect as failure in filling, whitening, or surface filmflaw and are sufficiently excellent in the aesthetic sense and design asa building material. Further, since the pressure exerted on thephotovoltaic elements is reduced, the solar cell modules of the examplesof the present invention are excellent not only in the initialelectrical characteristics, but also in those after the high temperatureand high humidity test and after the temperature/humidity cycle test,showing little change of conversion efficiency, less than 1% in eithercase. Therefore, the reliability is sufficient as a solar cell module.Further, there is no change in the external appearance after the varioustests, so that the appearance is also good. As for the scratchresistance, all the modules of the examples of the invention pass the5-pound test and thus have sufficient resistance against scratching fromthe outside. Namely, all the solar cell modules shown in the examplesare building materials having the workability equivalent to that of theordinary steel sheets, having the design property satisfying the needsfor the roof materials and wall materials, and being excellent in theaesthetic sense. Further, they also have long-term reliability.

On the other hand, Comparative Examples 1-1, 1-2, and 1-3 demonstrateexcellent workability equivalent to that of the examples. However,Comparative Example 1-1 has great damage of the photovoltaic elementsbecause the regions above the photovoltaic elements are directly pressedby the blade of the bender in processing with the bender. Thus, themodule of Comparative Example 1-1 shows a great lowering in conversionefficiency. As to the initial appearance of Comparative Example 1-1,much whitening is observed in the surface covering material. Thewhitening becomes worse after the various tests, whereby the conversionefficiency is further lowered.

In Comparative Examples 1-2 and 1-3, the great damage is also seen inthe elements because of the high pressure exerted on the photovoltaicelements on the occasion of press processing, so that lowering inconversion efficiency occurs. Since the mold directly touches thesurface, flaws are formed in the surface of solar cell module.Particularly, large flaws are formed in the portions where the edge ofthe mold contacts, whereby separation (peeling) is observed from suchportions after the environment test.

Next, in Comparative Example 1-1 where the flat-plate solar cell moduleafter module formation is stuck to the steel sheet as the roof materialpreliminarily processed, so as to have the bent portion, the number ofoperation steps increases, and the workability is thereby degraded. Inthe high temperature and high humidity test, peeling off occurs at theinterface of the adhesive stuck later, thus exhibiting great defects inappearance.

Example 2-1

The flat-plate solar cell module is made in the same manner as inExample 1-1, except that the back surface laminate film 606 is replacedby a lamination film of the total thickness 550 μm obtained byintegrally stacking an ethylene-vinyl acetate copolymer (vinyl acetate25 wt % and the thickness 225 μm) as an adhesive layer, which is thesame resin as the organic polymer resin on the light-receiving side, anda biaxially oriented polyethylene terephthalate film (PET) (100 μmthick) as an insulating film in the stacking order of EVA/PET/EVA.

[Processing with Roller Former]

Then the edge portions of the solar cell module are bent in the regionsnot including the photovoltaic elements by the roller former moldingmachine, as shown in FIG. 4A. In this way, the solar cell module isformed while preventing the rollers from touching the photovoltaicelement portions.

[Processing]

Then the support member is bent by the press molding machine,irrespective of presence or absence of the photovoltaic element, asshown in FIG. 4B. The press processing is done by placing the solar cellmodule between the lower mold having the projected portion and the uppermold having the depressed portion. At this time the press conditions areadjusted so that the peak strain of the flexible substrate of thephotovoltaic element is 0.6% (residual strain 0.4%).

In the last step, wires for taking the power out are attached to theback surface of the solar cell module. The support member ispreliminarily perforated in terminal-out portions of the solar cellgroup, and the positive and negative output terminals are taken outthrough the holes. Further, each terminal-out portion is provided with apolycarbonate junction box for insulation protection and waterproofness.Cables used are cable lines each having a connector at the tip.

Example 2-2

The press conditions are modified from those in Example 2-1 so that thepeak strain of the flexible substrate of the photovoltaic element is0.3% (residual strain 0.1%). The solar cell module is produced in thesame manner as in Example 2-1 except for the press conditions.

Example 2-3

The solar cell module is produced in the same manner as in Example 2-1except that a polyimide film is used for the substrate of thephotovoltaic elements.

Example 2-4

The solar cell module of Example 2-4 is shown in FIG. 8. Thephotovoltaic elements are produced in the same manner as in Example 2-1,and the other steps are described below.

[Cell Block]

Five of the elements produced above are connected in series to producethe solar cell block. The method for producing the solar cell block isthe same as in Example 2-1.

[Flat-plate Solar Cell Module]

The flat-plate-shaped solar cell module is produced using the above5-series solar cell block in the same manner as in Example 2-1.

[Bending of Edge Portions]

The four corners of the flat solar cell module are cut by corner shears.After that, the shorter edges are folded 180° and the longer edges arebent 90° on the light-receiving side by processing with the bender. Theheight of the upright portions in the bent portions of the longer edgesis 25 mm.

[Press Processing]

A curved portion is provided by press processing. The curved portion ismade by interposing the solar cell module between the lower mold havingthe projected portion and the upper mold having the depressed portion.The press processing is done so that the peak strain of the substrate ofphotovoltaic element is 0.6% (residual strain 0.4%).

Example 2-5

The solar cell module is produced in the same manner as in Example 2-4except that a polyimide film is used for the substrate of the,photovoltaic element.

Comparative Example 2-1

The solar cell module is produced in the same manner as in Example 2-1except that the press processing is done so that the peak strain of thesubstrate of the photovoltaic element is 0.9% (residual strain 0.7%).

Comparative Example 2-2

The solar cell module is produced in the same manner as in Example 2-1except that the press processing is done so that the peak strain of thesubstrate of photovoltaic element is 1.4% (residual strain 1.2%).

Comparative Example 2-3

The solar cell module is produced in the same manner as in Example 2-1except that the press processing is done so that the peak strain of thesubstrate of photovoltaic element is 4.8% (residual strain 4.4%).

Comparative Example 2-4

The solar cell module is produced in the same manner as in Example 2-3except that the press processing is done so that the photovoltaicelement is 1.4% (residual strain 1.2%).

Comparative Example 2-5

The solar cell module is produced in the same manner as in Example 2-4except that the press processing is done so that the peak strain of thesubstrate of photovoltaic element is 1.4% (residual strain 1.2%).

The solar cell modules are evaluated as to the following items. Theresults are shown in Table 2 below.

TABLE 2 After hi-temp and After temp/humid cycle HHFB HHRB Initialhi-humid test test low- low- Outdoor exposure external externalconversion external conversion illuminance illuminance 3 6 12Observation by appearance appearance efficiency appearance efficiencyVoc Voc months months months SEM Ex 2-1 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Ex 2-2 ◯ ◯⊚ ◯ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Ex 2-3 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Ex 2-4 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚⊚ ⊚ Ex 2-5 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Comp ⊚ ◯ ◯ ◯ ◯ Δ Δ ◯ Δ X X Ex 2-1 Comp◯ ◯ ◯ ◯ ◯ X X Δ X X X Ex 2-2 Comp X X Δ X Δ X X X X X X Ex 2-3 Comp ⊚ ◯◯ ◯ ◯ X X Δ X X X Ex 2-4 Comp ⊚ ◯ ◯ ◯ ◯ X X Δ X X X Ex 2-5

Initial Appearance

The solar cell modules (in the final form) are evaluated as to theinitial external appearance, including the failure in filling andsurface flaws of a solar cell. At the same time, they are also evaluatedin terms of the aesthetic sense as a building material and a roofmaterial. The evaluation results are shown in Table 2, based on thefollowing criteria.

⊚: No defect is present in the external appearance, and the module isalso excellent in the aesthetic sense as a building material and a roofmaterial.

∘: Some defects are present in the external appearance but pose noproblem in practical use.

×: Very large defects appear in the external appearance with greatfailure in filling and flaws in the surface, or the module is extremelydamaged in the aesthetic sense as a building material and a roofmaterial.

The high temperature and high humidity test and the temperature/humiditycycle test are conducted under the same test conditions and evaluationcriteria as described previously.

Forward Bias Under Storage at High Temperature and High Humidity (HHFBTest)

The solar cell modules are placed under the circumstance of 85° C./85%(relative humidity). In this case, light is prevented from entering thesamples either by keeping the inside of the test machine in alight-intercepting circumstance or by shielding the light-receivingsurfaces of the samples. Under this circumstance, wiring is so set thatthe optimum operating voltage (Vmp) can be applied in the forwarddirection of the internal PV circuit (diode component) in the solarcells, the voltage is kept for 2000 hours, then the solar cell modulesare taken out, low illuminance Voc (open-circuit voltage (Voc) underilluminance of 200 Lx) is measured for each cell of the photovoltaicelements, and a change rate thereof is calculated from the initial valuebefore the start of the test. The lowering in low-illuminance Vocindicates lowering in shunt resistance due to junction defects insidethe photovoltaic element. Namely, the lowering indicates an increase ininternal defects.

The evaluation results are shown in Table 2, based on the followingcriteria.

⊚: The change of low-illuminance Voc is less than 1.0%.

∘: The change of low-illuminance Voc is not less than 1.0% and less than3.0%.

Δ: The change of low-illuminance Voc is not less than 3.0% and less than5.0%.

×: The change of low-illuminance Voc is not less than 5.0%.

Reverse Bias Under Storage at High Temperature and High Humidity, (HHRBTest)

The solar cell modules are placed under the circumstance of 85° C./85%(relative humidity). In this case, the light is prevented from enteringthe samples either by keeping the inside of the test machine in alight-intercepting circumstance, or by shielding the light-receivingsurfaces of the samples. Under this circumstance, wiring is so set thatthe operation voltage (Vf) of the bypass diode can be applied in thereverse direction of the internal PV circuit (diode component) or thesolar cell, the voltage is kept for 2000 hours, the solar cell modulesare then taken out, the low-illuminance Voc (open-circuit voltage (Voc)under the illuminance 200 Lx) is measured for each cell of thephotovoltaic elements, and the change rate thereof is calculated fromthe initial value before the start of the test. The lowering inlow-illuminance Voc indicates lowering in shunt resistance due to thejunction defects inside the photovoltaic element. Namely, the loweringindicates an increase in internal defects.

The evaluation results are shown in Table 2, based on the followingcriteria.

⊚: The change of low-illuminance Voc is less than 1.0%.

∘: The change of low-illuminance Voc is not less than 1.0% and less than3.0%.

Δ: The change of low-illuminance Voc is not less than 3.0% and less than5.0%.

×: The change of low-illuminance Voc is not less than 5.0%.

Outside Exposure

The solar cell modules are set outdoors (on the outdoor exposure groundin the Ecology Research Center of CANON KABUSHIKI KAISHA, 1-1Kizugawadai 4-chome, Kizu-cho, Soraku-gun, Kyoto) and are evaluatedafter three months, six months, and twelve months. The low illuminanceVoc (the open-circuit voltage (Voc) under the illuminance 200 Lx) ismeasured for each of the photovoltaic elements, and the change ratethereof is calculated from the initial value before the start of thetest.

The evaluation is made based on the following criteria.

⊚: The change of low-illuminance Voc is less than 1.0%.

∘: The change of low-illuminance Voc is not less than 1.0% and less than3.0%.

Δ: The change of low-illuminance Voc is not less than 3.0% and less than5.0%.

×: The change of low-illuminance Voc is not less than 5.0%.

Observation by SEM

Portions that seem to have the highest strain are cut out of the solarcell modules and are observed by a scanning electron microscope (SEM).The evaluation is made based on the following criteria.

∘: No crack is observed in the surface of photovoltaic element.

×: Cracks are observed in the surface of photovoltaic element.

As apparent from Table 2, the solar cell modules of the examples of theinvention demonstrate good initial appearance and good appearance evenafter the high temperature and high humidity test and after thetemperature/humidity cycle test. In Example 2-2 where the residualstrain is adjusted to be as small as 0.1%, the resulting solar cellmodule gives the impression that the work is somewhat poor, but it is ofthe level posing no problem. From the aspect of electricalcharacteristics, they demonstrate no lowering in low-illuminance Voceven after the high temperature and high-humidity forward bias andreverse bias tests (HHFB and HHRB). They show no degradation ofperformance and no defect even after 12 months of outdoor exposure. Whenthe surfaces of the photovoltaic elements in the solar cell modules ofthe examples are observed by SEM, no crack is observed, which does notcontradict the above test results. Therefore, the solar cell modules areproduced with high reliability.

On the other hand, cracks are observed in observation by the SEM of thesolar cell module of Comparative Example 2-1, where the peak strainduring processing is 0.9% and the residual strain is 0.7%. The cracksare considered to be formed in the surface of the element when thephotovoltaic elements are subject to the strain of 0.9% duringprocessing. When this sample is subjected to the forward and reversebias tests, lowering in low-illuminance Voc occurs near 1500 hours. Inthe outdoor exposure the lowering in low-illuminance Voc takes placegradually from six months after exposure onset.

Further, in the solar cell modules of Comparative Examples 2-2, 2-4, and2-5 where the peak strain during processing is 1.4% and the residualstrain is 1.2%, many cracks are observed in the SEM observation. In theHHFB and HHRB tests, lowering in low-illuminance Voc takes place near1200 hours. In the outdoor exposure test the lowering in low-illuminanceVoc also occurs three months after exposure onset. In the appearanceafter the high temperature and high humidity test and after thetemperature/humidity cycle test, slight whitening of the coveringmaterial is observed, though it is of the level posing no problem. Inthe solar cell module of Comparative Example 2-3 where the peak strainduring processing is 4.8% and the residual strain is 4.4%, change of theinitial appearance after processing is observed visually on thephotovoltaic elements (color changed). A lot of cracks are alsorecognized in the observation by SEM, of course. In the HHFB and HHRBtests the lowering in low-illuminance Voc is also observed before 1000hours, which does not contradict the observation results of cracks.Further, in the appearance of the covering material, since whitening isalso recognized in the processed portions, and since the whitening willbecome more prominent after the high temperature and high humidity testand after the temperature/humidity cycle test, there is a problem in theaesthetic sense as a roof material.

According to the present invention, since the deformable region of thephotovoltaic element becomes clear, the product developing speed of awide variety of solar cell modules can be increased greatly. Further,since the regions above the photovoltaic elements can be freelyprocessed without degrading the characteristics of the solar cell, therecan be provided solar cell modules which are excellent in the aestheticsense and in design. The solar cell modules processed in this way becomesolar cell modules with high reliability for a long period.

What is claimed is:
 1. A method for manufacturing a solar cell modulecomprising a photovoltaic element comprising at least one photoactivesemiconductor layer on a flexible substrate, which comprises subjectingat least a part of the flexible substrate to tensile deformation in thedirection parallel to a surface of the substrate with a strain less thana critical strain to lower the fill factor of the photovoltaic element,thereby deforming the photovoltaic element.
 2. The method according toclaim 1, wherein the tensile deformation has a strain within a plasticdeformation range of the flexible substrate and less than the criticalstrain to lower the fill factor.
 3. The method according to claim 1,wherein the working means for generating the deformation comprises pressmolding.
 4. The method according to claim 1, wherein the working meansfor generating the deformation comprises applying a tensile force in thedirection parallel to the surface of the substrate.
 5. The methodaccording to claim 1, comprising covering at least a light-receivingsurface of the photovoltaic element with an organic polymer resin. 6.The method according to claim 1, comprising providing anon-light-receiving surface of the photovoltaic element with a supportmember.
 7. The method according to claim 6, comprising providing thesupport member with a strain within a plastic deformation range.
 8. Themethod according to claim 7, comprising forming a plastically deformedregion only in a portion of the support member not provided with thephotovoltaic element on the light-receiving surface side, whereby thesolar cell module is processed to thereby maintain a shape thereof. 9.The method according to claim 7, wherein the plastic deformation rangeis not less than 0.2%.
 10. The method according to claim 6, wherein thesupport member is of a metal.
 11. The method according to claim 1,comprising providing the outermost surface on the light-receivingsurface side of the solar cell module with a transparent resin filmlayer.
 12. The method according to claim 1, wherein the photoactivesemiconductor layer is of amorphous silicon.
 13. The method according toclaim 1, wherein the critical strain to lower the fill factor is 0.7%.14. The method according to claim 1, wherein the flexible substrate is aconductive substrate.
 15. The method according to claim 14, wherein theconductive substrate is of a stainless steel.
 16. The method accordingto claim 1, wherein the flexible substrate is a resin film.
 17. Themethod according to claim 1, wherein the solar cell module functionsalso as a building material.
 18. A solar cell module comprising aphotovoltaic element comprising at least one photoactive semiconductorlayer on a flexible substrate, wherein at least a part of the flexiblesubstrate is subjected to tensile deformation in the direction parallelto a surface of the substrate with a strain less than a critical strainto lower the fill factor of the photovoltaic element, whereby thephotovoltaic element is deformed.
 19. The solar cell module according toclaim 18, wherein the tensile deformation has a strain within a plasticdeformation range of the flexible substrate or a support member providedon a non-light-receiving surface side of the photovoltaic element andless than the critical strain to lower the fill factor.
 20. The solarcell module according to claim 18, wherein at least a light-receivingsurface of the photovoltaic element with an organic polymer resin. 21.The solar cell module according to claim 18, wherein anon-light-receiving surface of the photovoltaic element is provided witha support member.
 22. The solar cell module according to claim 21,wherein the support member has a strain within a plastic deformationrange.
 23. The solar cell module according to claim 22, a plasticallydeformed region is formed only in a portion of the support member notprovided with the photovoltaic element on the light-receiving surfaceside.
 24. The solar cell module according to claim 22, wherein theplastic deformation range is not less than 0.2%.
 25. The solar cellmodule according to claim 21, wherein the support member is of a metal.26. The solar cell module according to claim 18, wherein the outermostsurface on the light-receiving surface side of the solar cell module isprovided with a transparent resin film layer.
 27. The solar cell moduleaccording to claim 18, wherein the photoactive semiconductor layer is ofamorphous silicon.
 28. The solar cell module according to claim 18,wherein the critical strain to lower the fill factor is 0.7%.
 29. Thesolar cell module according to claim 18, wherein the flexible substrateis a conductive substrate.
 30. The solar cell module according to claim29, wherein the conductive substrate is of a stainless steel.
 31. Thesolar cell module according to claim 18, wherein the flexible substrateis a resin film.
 32. The solar cell module according to claim 18,wherein the solar cell module functions also as a building material. 33.A method for manufacturing a solar cell module comprising a photovoltaicelement comprising at least one photoactive semiconductor layer on aflexible substrate, which comprises subjecting at least a part of theflexible substrate to tensile deformation in the direction parallel to asurface of the substrate with a strain within a plastic deformationrange, thereby deforming the photovoltaic element.
 34. A method formanufacturing a solar cell module according to claim 33 wherein theplastic deformation range is not less than 0.2%.
 35. A solar cell modulecomprising a photovoltaic element comprising at least one photoactivesemiconductor layer on a flexible substrate, wherein at least a part ofthe flexible substrate is subjected to tensile deformation in thedirection parallel to a surface of the substrate with a strain within aplastic deformation range, whereby the photovoltaic element is deformed.36. The solar cell module according to claim 35 wherein the plasticdeformation range is not less than 0.2%.